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beancounter
 
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That oil groove is on the intake valve side...just looked at Bruce Anderson's book and its the same. I believe there is a hole drilled from the end of that groove down at an angle that hits the exhaust valve guide.
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Old 12-29-2009, 06:25 PM
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Max Sluiter
 
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Yes, the groove takes oil splashed above and channels it to the holes seen in the finned exhaust valve guide.
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Old 12-29-2009, 06:29 PM
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I recall something about oil being delivered to the exhaust valve stem from BA's book but I thought it was vague.

If that is the case, seems a simple mod.

Cool stuff.
Old 12-29-2009, 06:52 PM
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Quote:
Originally Posted by jwasbury View Post
That oil groove is on the intake valve side...just looked at Bruce Anderson's book and its the same. I believe there is a hole drilled from the end of that groove down at an angle that hits the exhaust valve guide.
I think you have got it.

My guess:

The spray bar sprays the cam, the cam flips oil toward the intake valve, oil runs down across the grove which guides oil down through a hole to the exhaust valve stem.

Heat at the stem helps to draw the oil in.

Oil at the guide bridges the gap to the stem and helps the heat transfer from the valve to the guide.


As our heads are basically oil cooled I wonder if it makes sense to increase the size of the orifices in the spray bar like Porsche did to the piston squirters?

I am thinking we do not want to run the 3.2 Carrera oil limiters that may come with a tensioner kit.
Old 12-30-2009, 05:56 AM
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Just want to add something about the cam spray bars.

I've looked at mine closely because 2 of the holes in my passenger side spray bar were clogged when I bought my car.

I've only been able to find 3 oil holes in each spray bar, one across from each cylinders valve train and there's only one spray bar in the top middle section of each cam tower.
The 3 oil holes in each spray bar point straight up vertcal and they probably wouldn't be able to cover everything evenly in the entire valve train if they sprayed sideways toward the camshaft or right at them with only 3 oil holes.

The oil comes out of the 3 holes in a straight stream of oil straight upwards [ take off the upper valve cover and start the car or crank the starter motor and watch!] and ricochets off the inside of the angled valve cover and splatters spreading out all over the camshaft lobes, rocker arms and shafts, valve springs, retainers and stems, and everything else in there lubricating and cooling everything.

I've heard the white teflon valve seals are preferred over the tighter dark colored rubber ones because they let a little more oil past to lubricate the guides and valve stems.

I wonder if anyone makes finned exhaust valve guides for sale and if it would be a good thing on a street car.
Doesn't look like a valve seal could be installed on the finned valve guide in the picture above so there is a good chance of a bigger cloud of oil smoke when starting the car after it sits overnight with those installed.
I'm guessing that because the bottom of the crankcase and the lower half of the cam towers fill with oil as it drains back into the case from the oil tank overnight.
If your oil tank level is towards the top of the safe range when running hot and then you take the upper valve cover off after the motor has sat 12 hours or so and look down in there with a flashlight you can the oil level in the bottom of the cam tower is halfway up the inside surface of the lower rocker cover so it is possible part of the exhaust valve stems and maybe the some exhaust valve guides are submerged in oil at that point.

The possibility of the oil level in the case and cam towers submerging the exhaust valve stems after sitting overnight also depends on how much oil is in the motor and oil tank, and some people like to run that at the low mark on the dipstick to lessen oil smoke on startup.

just some more thoughts...
Old 12-30-2009, 08:18 AM
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Can you post a picture of the spraybars? Also, I read that the 935"s used the hollow cams with an oil feed from the bearing.
Old 12-30-2009, 09:07 AM
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I don't have a pic of the spray bar holes, but...
Everytime I adjust the valves I check that the cam spray bar holes are clear and shooting oil straight up and they're not clogged.

I don't like cleaning motor oil out of the AC condensor fins and rows and everywhere else it makes a mess when starting the car with the upper valve covers off... Did that after the first time and decided a better way to check that the 3 spray bar holes are clear is to completely clean the upper valve cover and slide it onto the studs and crank the motor over on the starter motor with the fuel pumps off for a couple seconds after getting oil pressure.

Then slide the upper valve cover off the studs and look at the 3 oil splash marks on the inside of the upper valve cover from the oil that shot straight up at it from the 3 cam spray bar holes.

Here's a pic of the inside of my upper valve covers showing 3 oil splash marks from the 3 vertical cam spray bar holes.
When all 3 oil splash marks look about the same after 2 seconds of starter motor cranking I believe the cam spray bar holes are clear and good to go.
Old 12-30-2009, 09:40 AM
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Good one, thanks
Old 12-30-2009, 10:34 AM
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So if we do the oil to exhaust valve mod, how dose that play in with the valve stem seals?


Cool think checking the spray bar with valve adjustments. Lost a couple of lobes on my C2 Turbo once. Very smart!
Old 12-30-2009, 12:54 PM
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slightly off topic (but back to the original topic).

All valve guides need replacing, however my pistons and cylinders are in excellent condition (rings should be replaced though).

Head studs are non-magnetic, so I assumed Dilivar but are all in good shape. I decided to go with steel studs, but am still going back and forth on that one. I may end up biting the bullet and getting ARP.

You will all be impressed that the only 'while you are in there' that I am doing is a set of SC cams to complement the other common turbo mods on the car.Turns out to be less than 10% of the total rebuild cost... I'm proud of myself.

My main goals was to eliminate the smoking when hard on the gas, as well as the various oil leaks which were getting really bad. The turbo was shot also BTW.
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Old 01-08-2010, 03:32 PM
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Also back on topic, I didn't see a lot of input here on rebuilding your turbo. Depending on the condition, rebuilding can be a simple matter. I say this, assuming that both the compressor and turbin wheels and housing are in good shape....nothing bent or missing. You can take the turbo apart in all of 20 minutes and buy new seals, thrust plate, and journal bearings...and install them without having to rebalance everything (must mark the original position of both wheels on the shaft). If the bearing housing is worn but the shaft is ok, you can purchase oversized bearings and ream the housing out to the new dimension. If the shaft is worn, then you're stuck with replacing it and having it all rebalanced.

Again, it all depends on the condition of the components. I'm in the process of doing a rebuild as we speak. Finding the parts...well, they're out there, but not real plentiful. Well less than $100, in my case anyway. Been getting some good input from a forum member who's got a lot of experience.
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Old 01-08-2010, 04:53 PM
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Thanks Mark. I didn't mention the rebuild of the turbo much as it seems to be 'taboo' to rebuild your own turbo. I bought a rebuild kit and have most of it apart already (I've done it before on a different turbo) but I'm having a hard time with the turbine housing and getting it off. Will tackle that tomorrow.

I'll have to check the housing to make sure it's still ok. There was enough shaft play that I could feel it without it being on a dial indicator, so I knew it had to be done. Only had 10-15K miles on it though since new.
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Old 01-08-2010, 05:23 PM
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Quote:
Originally Posted by mark '87 930 View Post
Thanks Mark. I didn't mention the rebuild of the turbo much as it seems to be 'taboo' to rebuild your own turbo. I bought a rebuild kit and have most of it apart already (I've done it before on a different turbo) but I'm having a hard time with the turbine housing and getting it off. Will tackle that tomorrow.

I'll have to check the housing to make sure it's still ok. There was enough shaft play that I could feel it without it being on a dial indicator, so I knew it had to be done. Only had 10-15K miles on it though since new.
Two types of play to look for....radial and run-out. Run-out should be almost non-existant (I don't know the specs), and excess would indicate the thrust plate is worn. Radial, when applying sideways pressure to either end of the shaft, definitely should not cause contact of the wheel with the housing. Apply pressure and slide a feeler gauge between the wheel and the housing. Anything less than .005 inches clearance would indicate new bearings at the least, because the balance would be compromised and risk rubbing on the housing. I am by far not an expert and as with everything I start by learning from others and then by doing. Get everything apart and look for signs of wear. Stock sizing and dimensions are available to compare your wear against.

I think we've all been led to believe that turbo rebuilding is a taboo subject for the DIY'er. That's true if rebalancing is needed. Otherwise, these things are pretty straighforward. Even brand new, there will be a lot more "play" than a person would think, given that the bearings are sized to allow the shaft to ride freely in a layer of oil by design.

I could be all wet - and I'm sure I'll hear about it from my esteemed friends out there, but suffice it to say that other's have successfully done this. I like pushing the envelop and challenging conventional wisdom...that's my nature.
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Old 01-08-2010, 05:57 PM
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There's some good 3K information in this link: Design and Function of a Turbocharger - Bearing system | TurboDriven.com - BorgWarner Turbo Systems

You should feel some lateral or sideways play of the turbo shaft because the 2 sleeve bearings on the shaft are full floating in oil.
They have oil clearance on the inside and outside and they rotate at about half shaft speed in oil inside the bearing housing never allowing metal to metal contact.
There should be no noticeable axial play with your fingers. If there is the thrust bearing is probably worn.

Also you should have some way to check for wear in the piston ring grooves or lands on the shaft. If they are worn or eroded and full of coked carbonized oil the turbo is going to still leak and burn oil at times after you reassemble it.
The piston ring oil seals are compressed and clamped in place by the bearing housing when the shaft is installed in it and they do not rotate.

Marking an inducer and exducer blade with a sharpee pen or magic marker in relation to the shaft works to realign them in balance when reinstalling the same parts on the same shaft but the nut that holds the compressor wheel on the shaft usually has a side or two ground away when it's magnetized and balanced in a VSR balancing machine so when it's all back together and torqued down that nut would have to be in the exact same position on the shaft threads or the high speed balance will be off.

Where did you get the rebuild kit? ..and what color locking paint is on the compressor wheel nut?

I'm not a turbo expert either but I've had alot of very expensive repetitive experiences with one and I wouldn't try to rebuild one if I expected it to last. I don't have the equipment to do it right and I've never done it before.
Old 01-08-2010, 08:13 PM
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There was significant axial play, enough for me to feel it easily by hand. This is why I decided to get a rebuild kit (purchased from a local turbo rebuilder). The locking paint on the wheel nut was green. I marked both the wheel and the nut, as well as where it aligns on the shaft. The intention is to replace all internals and reassemble as it was when I first took it apart.

Thanks everyone for the input. keep it comin'.
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Old 01-08-2010, 10:04 PM
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this is a pic of my 935 heads with the oiling modification, I would not recommend this except on a all out track application. This helps pull heat out of the valves by having a oil passage drilled thru the valve guide midway, its just not needed on a street build.




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Old 01-08-2010, 11:14 PM
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Max Sluiter
 
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Do you have any data from track days before and after this mod? Or did you do your race engine all at once. Is there any noticable performance advantage or is it only seen through improved reliability and decreased wear upon overhaul? It would be cool to see a car with this modificationo using a cylinder head temperature sensor and logging the data throughout a session on the track.

This seems like a simple machining operation- easier than twin-plugging. While not necessary as on a racing engine, I would think a street engine could benefit and I see no downsides to doing it "while you are in there."

Cool stuff, thanks for posting. Sorry I stole your photo.
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Old 01-08-2010, 11:31 PM
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Quote:
Originally Posted by mark '87 930 View Post
Thanks Mark. I didn't mention the rebuild of the turbo much as it seems to be 'taboo' to rebuild your own turbo. I bought a rebuild kit and have most of it apart already (I've done it before on a different turbo) but I'm having a hard time with the turbine housing and getting it off. Will tackle that tomorrow.

I'll have to check the housing to make sure it's still ok. There was enough shaft play that I could feel it without it being on a dial indicator, so I knew it had to be done. Only had 10-15K miles on it though since new.
Hi Mark -

Please take these comments as meant to be constructive. It’s very unfortunate you tore this turbo down. With only 10-15k miles odds are there was nothing wrong with it.

Regarding inspection, the industry standard is; if the individual wheels are not rubbing their housings it’s probably OK. If the blades have no impact marks it’s probably OK. This rule does not catch them all but roughly 98%.

It’s true that turbos are often successfully rebuilt by a DIYer, but then statistically most didn’t need to be torn down in the first place. While a turbo is very simple in concept it must be perfectly right in a few critical areas when reassembled. If not done right it will fail in short order, then you will have a bad core to trade in for a new turbo.

At this stage I suggest you collect the pieces and take them to an authorized shop. I find turbos fascinating, ask the shop to allow you to witness what they are doing and explain these critical areas to you.

If you wish to dig into a turbo the 3LDZ is a robust old design that should give you the experience and probably survive for use as a shakedown turbo.

Last edited by copbait73; 01-09-2010 at 01:01 PM..
Old 01-09-2010, 12:54 PM
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Rebuild a Turbo?

Mark,
I was forced to rebuild mine due to FOD. There was very little play, but the blades were damaged as shown below:


I tried to find an exhaust tubine wheel and shaft but I had no luck. In my search I found Durabuilt Turbos and they had a cartridge for my stock K27 for $527. The cartridge consists of both turbine and compressor wheels and the center section. Since it comes pre-balanced, it is a bolt-in replacement.

One thing I learned in the process is that you have to heat the compressor wheel to remove it from the shaft if you are going to get to the bearings and seals for a rebuild. If you can put it together exactly as it came apart the balancing should be close.

Having said that, my local turbo guy, Tim's Turbos has a Hein balancing machine that is so sensitive that I swear a fingerprint on the compressor wheel will throw it off, I'm just sayin'.

I have my old center section and compressor wheel if anyone wants it cheap, the turbine wheel is junk, of course.

Good luck,
Mark
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Old 01-09-2010, 03:15 PM
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I'm done with the rebuild of the turbo. they are straight forward, I was simply having issues initially with the turbine housing and removing it. Thank god for friends with machine shops, building tools on demand to get your to where you want to go (thanks to Porsche Monkey). Everything was in descent shape, but it definitely needed a rebuild due to run-out play. It took about 1 hour to clean and re-assemble everything the way it was.

Now back to cleaning the remainder of the engine bits/transmission.. and I'm waiting for parts.
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Last edited by mark '87 930; 01-10-2010 at 04:53 PM..
Old 01-10-2010, 04:49 PM
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